This invention relates to a needleless injection system which includes a prefilled cartridge.
One of the problems inherently present in the packaging of liquid parenteral drugs is that there is not enough biocompatibility data about the interaction between those drugs and thermoplastic containers. While plastic is commonly used in many injection devices, most parenteral drugs cannot be exposed to most plastics other than for a short period immediately prior to the injection. This is because the drug or injectate may chemically react with the plastic, or cause materials in the plastic to leach into the injectate, thereby introducing impurities in the drug. In periods of extended storage, such exposure to a plastic container may result in degradation of the drug. For these reasons, the pharmaceutical industry normally avoids the storage of injectate in some thermoplastic materials such as polypropylene, which is commonly used in syringes and related injection paraphernalia. Similarly, there is no long term biocompatibility data on engineering or high strength thermoplastics, such as polycarbonate, which is the plastic most commonly used in needleless injection systems.
For this reason, injectates are typically stored in glass vials. Immediately prior to injection, the injectate chamber of a needleless injection system is filled from a glass vial containing the drug. This normally requires the use of a vial adapter, sometimes referred to as a blunt fill device, or an access needle which pierces the protective membrane over the top of the vial and then directs injectate down into the chamber or cartridge of the needleless injection system.
There are a number of drawbacks with this conventional approach. For example, the extra step of having to transfer the drug from the glass vial to the needleless injection system is time consuming and can be troublesome to a patient who is trying to administer the drug at home and who may have physical infirmities. Even for those who are not infirm, an adapter must be on-hand, and it must be sterile to prevent contamination of the injectate. The adapter typically includes a transfer needle with a sharp point at one end to pierce the vial membrane, and that can lead to injury, to unintended introduction of the injectate into the handling personnel or administrator, and/or to contamination of the injectate. This extra step of filling the needleless injection system immediately prior to injection also brings about the possibility of leakage and waste of injectate and, if improperly performed, can introduce air into the injection system. The introduction of air presents difficulties in a needleless injection system, because unlike a conventional needle and syringe system, it is not easy to bleed air out of the chamber of a needleless device. Therefore, firing the injection system with a portion of its chamber filled with air results in a lower dosage being injected into the patient. It is also possible that the injection may take place at an improper pressure. One advantage of the needleless injection systems of Bioject, Inc., assignee of this patent, is that they are able to inject a precisely predetermined amount of injectate at a predetermined, precise location in the tissue of the patient. The introduction of air may make it difficult to achieve such precision.
Accordingly, it is an object of the present invention to provide for the prefilling of a cartridge to be used in a needleless injection system.